Immune regulation of complement components will be studied in F1 hybrids from matings of normal (homozygous) males and females homozygous for specific genetic defects in single complement components. Specific chronic suppression of the fifth component of complement (C5) can be accomplished in (C5 negative C5 positive)F1 mice by 1. neonatal administration of anti-C5 antibody or 2. by neonatal administration of (C5 negative C5 negative) parental cells. The major goal of the experiments outlined in this proposal is to elucidate the mechanisms of anbibody and cell mediated regulations of complement components. In vitro and in vivo experiments will be carried out with whole cell populations, fractionated subpopulations and purified antibodies to determine 1.) relevant cell types and their genetic control, 2.) the role of antibody and other humoral regulatory factors, 3.) the role of the state of immunity of mothers and cell donors and 4.) the influence of genetic polymorphism of the complement component being suppressed. Since complement components are relatively homogeneous proteins under simple genetic control, they offer a unique model with which to extend studies of immune regulation into systems consisting of nonlymphoid cell products.